The present invention relates to a sputtering target and/or a coil that can increase the degree of vacuum during sputtering, have uniform and fine structures, give stable plasma, and allow production of a film having excellent uniformity, and relates to a method of producing such a target or a coil.
Recent years, sputtering is used for forming a coating of, for example, a metal or a ceramic material in various fields such as electronics, corrosion-resistant materials, decorations, catalysts, and production of cutting/abrasive materials and wear-resistant materials.
Though sputtering itself is a well-known method, recently, in particular, in the electronics field, sputtering targets suitable for forming coatings with complicated shapes, circuits, barrier films, or other films have been being required.
In general, a target is produced from an ingot or billet prepared by melting/casting a metal, an alloy, or another material through hot forging, annealing (heat treatment), and processing of rolling and finishing (e.g., mechanical or polishing).
When sputtering thus produced target, further mechanical processing such as grinding or polishing to the target surface is performed on the target to smoothen and allow formation of a uniform film having stable characteristics with fewer occurrences of arcing and particles.
However, there was a problem in sputtering the target that the degree of vacuum in a vacuum chamber does not increase. And investigation for causes revealed that the hydrogen partial pressure in the vacuum chamber is high.
After further investigation for causes, it was revealed that the surface of a target used occludes a large volume of hydrogen and that this hydrogen vaporizes during sputtering to increase the hydrogen partial pressure in the chamber.
In addition, in recent sputtering technology, a coil is disposed between a sputtering target and a substrate to increase the plasma density and allow flying sputtering particles to direct toward the substrate as much as possible. As a result, the sputtering rate is increased, and the uniformity of the film is improved. Thus, the quality of the film deposited on the substrate is comprehensively enhanced.
The material of the coil is usually the same as that of the target or a part of the material constituting a sputtered film deposited on a substrate, but is not particularly limited as long as the material of the coil does not contaminate the thin film on the substrate. The coil may have any shape, a circular or spiral shape, for example. A plurality of coils may be disposed in multiple stages.
The present inventors have struggled with a reduction in hydrogen content on the surface of a target and/or a coil, and have had a belief that hydrogen occlusion occurs in the process of producing the target and/or the coil, particularly, in cutting and polishing processing.
In conventional mechanical processing (cutting and polishing processing), since the processing efficiency is valued, a water-soluble oil such as emulsion, soluble oil, or solution is used having excellent coolability to perform processing at high speed. As long as based on this idea, a countermeasure against the problem of an unsatisfactory degree of vacuum could not be solved. That is, the volume of hydrogen could not be necessarily reduced in conventional mechanical processing of the surfaces of a target and a coil.
Thus, the present inventors have studied documents relating to the surface of a target and/or a coil or hydrogen present in a target and/or a coil. And, they have found the following documents.
Patent Literature 1 describes that a reduction in hydrogen content of a surface to 50 ppm or less can prevent generation of nodules and decrease the number of particles. In addition, a reduction in total volume of Si, Al, Co, Ni, and B to 500 ppm or less can prevent micro-arcing on the erosion surface and can prevent occurrence of nodules and decrease the number of particles. There are descriptions of examples using Ti, Ta, Cu, and Al as the materials.
However, the problem is understood as only an issue of the composition of the target. Thus it does not provide a fundamental solution for the problem that the degree of vacuum in a vacuum chamber is not enhanced. And there is a problem that how the volume of hydrogen is decreased during processing of a target is not technically disclosed or suggested.
Patent Literature 2 discloses that projections occur on the target surface by aluminum oxide and hydrogen to cause abnormal electrical discharge during sputtering and that the volumes of the oxide and the hydrogen gas are reduced to 3 ppm or less and 0.1 ppm or less, respectively. However, in this case also, the problem is understood as only an issue of the composition of a target. Thus it does not provide a fundamental solution for the problem that the degree of vacuum in a vacuum chamber is not enhanced. And there is a problem that how the volume of hydrogen is decreased during processing of a target is not technically disclosed or suggested.
Patent Literature 3 discloses that hydrogen contained in a Ta sputtering target and a Ta film formed on a TaN film causes a tendency of peeling of the film and an increase in the number of particles and that the hydrogen concentration in the Ta is therefore decreased to 20 ppm or less. However, in this case also, the problem is understood as only an issue of the composition of a target. Thus it does not provide a fundamental solution for the problem that the degree of vacuum in a vacuum chamber is not enhanced. And there is a problem that how the volume of hydrogen is decreased during processing of a target is not technically disclosed or suggested.
Patent Literature 4 discloses that the oxygen content is 150 ppm or less, that oxygen is generated during sputtering to disadvantageously affect the film characteristics such as a resistance value of the film to be formed, and that a decrease in the number of generated particles and a decrease in oxygen content conflict with each other. This does not directly relate to hydrogen, besides, in this case also, the problem is understood as only an issue of the composition of a target. Thus it does not provide a fundamental solution for the problem that the degree of vacuum in a vacuum chamber is not enhanced. And there is a problem that how the volume of hydrogen is decreased during processing of a target is not technically disclosed or suggested.
Patent Literature 5 discloses a sputtering target composed of Cr as a main component and 10 to 50% by atom of Al, Si, Ti, Zr, Hf, V, Nb, Ta, W, Mo, and B and discloses that a hard nitride film with high adhesion can be formed by regulating the total content of oxygen, carbon, sulfur, and hydrogen to 3000 ppm or less. This is not understood as only a problem of hydrogen, but understood as an issue of the composition of a target; thus it does not provide a fundamental solution for the problem that the degree of vacuum in a vacuum chamber is not enhanced. And there is a problem that how the volume of hydrogen is decreased during processing of a target is not technically disclosed or suggested.
Patent Literature 6 discloses a sputtering target for a metal alloy with a high melting point, where the target includes W, Mo, Ti, or Ta as the material thereof. However, it does not provide a fundamental solution for the problem that the degree of vacuum in a vacuum chamber is not enhanced. And there is a problem that how the volume of hydrogen is decreased during processing of a target is not technically disclosed or suggested.
Patent Literature 7 describes that the oxygen level of a sputtering target is decreased through scavenging by hydrogen during synthesis of a metallic structure. This case also does not provide a fundamental solution for the problem that the degree of vacuum in a vacuum chamber is not enhanced. And there is a problem that how the volume of hydrogen is decreased during processing of a target is not technically disclosed or suggested.
Patent Literature 8 discloses a Ti-containing high purity Ta sintered target and describes that hydrides of Ta and Ti are easily pulverized into a powder having a suitable particle size for the subsequent sintering, and dehydrogenation gives a surface-active powder to accelerate sintering and also prevent contamination by oxygen. However, this case also does not provide a fundamental solution for the problem that the degree of vacuum in a vacuum chamber is not enhanced. And there is a problem that how the volume of hydrogen is decreased during processing of a target is not technically disclosed or suggested.
Patent Literature 9 describes a surface treatment process by mechanically polishing the inner surface of a vacuum container in the presence of a hydrogen atom-free liquid medium. According to the descriptions, the main reasons that this surface treatment process is required are as follows: one is in order to decrease the degree of vacuum achieved since hydrogen is diffused and desorbed from the surface of a vacuum member and the inner surface, and is gradually released in the vacuum system. The other is that it is necessary to reduce the volume of hydrogen and moisture adsorbed, occluded, or solid-solubilized in the vacuum container and the device, since a sufficient acceleration cannot be achieved if hydrogen is occluded or solid-solubilized in the member in a device such as an accelerating cavity.
The inner walls of these vacuum devices and equipment installed inside thereof are generally not worn over a long period of time. Therefore, once hydrogen and moisture that are adsorbed, occluded, or solid-solubilized are removed by mechanical polishing, hydrogen and moisture will not be newly adsorbed, occluded, or solid-solubilized; as long as the devices are not disposed under specific environment.
However, since the sputtering target is an expendable component and the target itself is worn with lapse of time due to erosion, that is, a new erosion surface appears, an idea that the target itself directly affects the degree of vacuum during sputtering does not occur. It is believed by common sense that hydrogen is constantly released from the start and with the progress of erosion of the target.
In that sense, when inclusion of hydrogen or moisture is a problem, it is necessary to reduce the volume of hydrogen or moisture of the entire target (the entire area to be eroded), and the idea that merely mechanical polishing of the surface can solve the problem is not conceivable.
From this viewpoint, Patent Literature 9 describes a solution that prevents adsorption, occlusion, and solid-solution of hydrogen and moisture during polishing of the inside of a vacuum container and equipment in an initial stage. Since the device and equipment are used for a relatively long time after the conduction of the process, it is hardly conceivable that the process is applicable to a sputtering target which is frequently replaced. Thus, this document does not disclose or suggest the present invention.
Patent Literature 10 discloses a method of polishing the surface of a hydrogen-occluding metal using a grinding fluid having a moisture content controlled to a predetermined level or less. It is described that according to this method of grinding a hydrogen-occluding metal, the hydrogen volume in the hydrogen-occluding metal of which surface is ground is extremely small to show a sufficient effect on the original use of the hydrogen-occluding metal.
In general, the hydrogen-occluding metal stores hydrogen or heat through a reaction of generating a hydride and has excellent functions of occluding hydrogen by taking hydrogen into gaps between metal atoms and of releasing the taken hydrogen.
Patent Literature 10 describes that hydrogen derived from moisture is prevented from being absorbed in the hydrogen-occluding metal. This is the effect that the use of a grinding fluid containing less moisture in volume can prevent an active surface newly generated by polishing the surface of a hydrogen-occluding metal from repeated exposure directly to moisture in the grinding fluid and the atmosphere. However, this is merely preventing the function of the hydrogen-occluding metal temporarily.
Since the sputtering target is an expendable component and the target itself is worn with lapse of time due to erosion, that is, a new erosion surface appears, an idea that the target itself directly affects the degree of vacuum during sputtering does not occur. It is believed by common sense that hydrogen is constantly released from the start and with the progress of erosion of the target.
In this sense, when inclusion of hydrogen or moisture is a problem, it is necessary to reduce the volume of hydrogen or moisture of the entire target (the entire area to be eroded), and the idea that merely mechanical polishing of the surface can solve the problem is not conceivable.
From this viewpoint, Patent Literature 10 describes a solution that prevents adsorption, occlusion, and solid-solution of hydrogen and moisture during polishing. However, the sputtering target, which thereafter is used for a long time with repetition of occlusion and release of hydrogen, it is hardly conceivable that the process is applicable to a sputtering target which is frequently replaced. Thus, the document does not disclose or suggest the present invention.
Furthermore, Patent Literature 11 discloses a technology using high purity copper as a coil for sputtering deposition. In this case, the purpose is removal of defects in a film deposited on a substrate.    [Patent Literature 1] Japanese Patent Laid-Open Publication No. H11-1766    [Patent Literature 2] Japanese Patent Laid-Open Publication No. H08-13141    [Patent Literature 3] Japanese Patent Laid-Open Publication No. H11-080942    [Patent Literature 4] Japanese Patent Laid-Open Publication No. H06-322529    [Patent Literature 5] Japanese Patent Laid-Open Publication No. 2003-226963    [Patent Literature 6] Japanese Patent Laid-Open Publication No. H03-257158    [Patent Literature 7] Japanese Patent Laid-Open Publication No. 2001-73128    [Patent Literature 8] Japanese Patent Laid-Open Publication No. H01-290766    [Patent Literature 9] Japanese Patent No. 4184344    [Patent Literature 10] Japanese Patent Laid-Open Publication No. H11-19853    [Patent Literature 11] Japanese Patent Laid-Open Publication No. 2001-214264